Changes in the functional characteristics of glutamatergic synapses are thought to underlie basic processes of brain development and learning. The overall goal of the proposed project is to define interrelationships between glutamate receptor activation, protein synthesis, and dendritic spine shape that may be involved in the stabilization of such synaptic changes. The proposed studies have three specific aims: 1) to determine the degree of spatial correspondence between synapses undergoing activity at a level associated with functional change and sites of protein synthesis via mechanisms that involve cap-dependent and internal ribosomal entry sequence (IRES) mechanisms of translation; 2) to define the relative contributions of cap-dependent and internal initiation mechanisms of translation to activity-induced protein synthesis in dendrites; and, 3) to determine the general interdependence between translation and spine structure, and to test the specific role of protein synthesis in the formation of abnormally long spines seen in a fragile X syndrome model and with stimulation of metabotropic glutamate receptors. Novel fluorescent reagents have been developed to conduct these studies, including a marker, based on fluorescence resonance energy transfer (FRET), for marking synapses undergoing plastic change, and several fluorescent reporters of cap-dependent and IRES mediated dendritic translation. The studies will be conducted in dissociated and organotypic slice cultures of hippocampus, and will use a pseudoconfocal fluorescence microscope system controlled by a software package that includes image analysis tools for quantification of fluorescent reporter expression. The proposed experiments should provide valuable information for our understanding of how dendritic protein synthesis relates to synaptic activity, structure, and forms of efficacy change thought to underlie global processes of brain development, learning, and memory.